High temperature liquid metal pipe furnaces



INVENTOR @im 9L 722454.42/ ATTORNEYS Oct. 27, 191() A.-v. GRossE HIGHTEMPERATURE LIQUID METAL PIPE FURNACES 3 Sheets-Sheet l ARISTID V.GROSSE ELECTR|CAL POWER SOURCE ct. 27, 1910 A, v, GRossE 3,536,818

HIGH TEMPERATURE LIQUID METAL PIPE FURNACES Filed Nov. 50, 1967 y 3Sheets-Sheet Z t i s l l I s s e INVENTOR ARISTID V- GROSSE 6a/L Geom@wim-em ATTORNEYS United States Patent O 3,536,818 HIGH TEMPERATURELIQUID METAL PIPE FURNACES Aristid V. Grosse, Haverford, Pa., assignor,by mesne assignments, to Reynolds Metals Company, Richmond, Va., acorporation of Delaware Filed Nov. 30, 1967, Ser. No. 686,924

Int. Cl. Hb 3/62 U.S. Cl. 13-21 15 Claims ABSTRACT OF THE DISCLOSURE Ahollow pipe whose walls are formed of concentric cylinders of differentsubstances may serve as a container for or as a furnace generating hightemperatures on the order of 3000 K. The substances of each cylinderwhich may be solid at start up are chosen to have liquid densities sothat when the substances melt and the pipe is rotated to rim thesubstances, the layers maintain their desired relationships. One of thecylindrical layers may include uranium disposed so as to support aneutron chain reaction. Other cylindrical layers are provided to protectthe uranium against loss due to vaporization and reaction with elementspassing through the pipe and to support the uranium layer even when aliquid. Practical applications of the high temperature apparatus includerocketry, MHD generation, and generally any process requiring hightemperatures.

This invention relates to apparatus for confining high temperaturemedia, and more specically to methods and apparatus for obtaining,containing and maintaining high temperatures in the center of hollowliquid metal pipes.

BACKGROUND OF THE INVENTION High temperature research dealing withsubstances at temperatures on the order of 3000 to 20,000" K. involvesthe sciences of chemistry, physics, metallurgy and ceramics. Very fewcompounds, of the millions of known chemical compounds, are stable attemperatures in these ranges. Very few remain in a solid state above3000 K. Confinement of gases at these high temperatures is relativelyeasy because they are Very rareied. On the other hand, confinement ofliquids or liquids and solids, or, generally, matter in the condensedstate at such high ternperatures poses a much more dicult problem. It isthis containment of liquids at high temperatures that is the subjectmatter of this invention.

A corollary problem is to generate temperatures of this magnitudethrough methods which can be controlled. Where the high temperature isproduced by chemical reactions, thermally stable reaction products mustbe provided. It is known that these can be achieved in several ways suchas by combustion of metals and oxygen; through combustion of gaseousmixtures; or through plasma jets. Coniining or containing such chemicalsubstances at the temperatures achieved is a limitation on the time thereaction can be allowed to continue.

In my U.S. Pat. No. 2,997,006, issued on Aug. 22, 1961, the combustionof a highly exothermic metal and oxygen in a rotating furnace isdescribed. Upon rotation of the furnace, the continuous mass of moltenmetal spreads to cover the entire inner surface of the refractorylining, forming, what has been characterized as a liquid pipe. Alimiting factor of the furnace is the dissociation temperature of therefractory material which lines the reaction area.

There is described in Science, May 17, 1963, vol. 140, No. 3568, atpages 781-789, and in the Journal of the American Chemical Society, vol.84, page 3209 (1962) the heating of liquid metals in the form of aliquid pipe by ICC means of an electric current, a plasma jet, and achemical reaction. In the first-mentioned article, it was also proposedto incorporate fssionable material as the heat source in a liquid pipefor the purpose of producing rocket thrust.

High temperature plasma jets with a noble gas such as helium or argonhaving temperatures in the range of 5000o to 15,000 K. have been used asa source of heat for a centrifugal furnace. Such a furnace may consistof a steel cylinder surrounded by a coolant jacket and rotated to rimthe contained material when liquid. The interior of the steel cylindermay be filled with an insulating material such as alumina bubbles orThermax (TM) carbon.

Major problems inherent in attempting to make practical use of suchliquid pipes include the evaporation of the liquid metals into a gasstream which may flow through the device, chemical reactions between thevarious adjacent materials making up or contacting the pipes, andmiscibility of these adjacent layers at the high temperatures.

Accordingly, the primary object of the present invention is to providenovel methods and apparatus for obtaining, and/or maintaining hightemperatures.

Another object is to provide a novel multi-layered pipe which can berotated to maintain a hollow pipe coniiguration even when the materialsare in a liquid state. The means of generating the high temperature maybe eX- ternal of the hollow pipe, or the materials forming the walls inthe pipe may contribute in whole or in part to the generation of thetemperatures achieved.

A still further object is to provide novel methods and apparatusallowing the attainment of higher temperatures than has heretofore beenpossible, particularly with nuclear chain reactions by providing acylindrical layer containing uranium to support the chain reactions. Anovel protective layer on the surface of the uranium to reduce the rateof evaporation of the uranium may be provided along with a layer ofsupporting material which has a liquid density sufficiently high tofloat the uranium when in a liquid state.

Yet another object is to provide a liquid pipe having at least threeconcentric layers of metallic or non-metallic substances which, when ina liquid state, maintain the desired configuration to thereby allowheating of the interior of the pipe to higher temperatures than wouldotherwise be possible. By passing a fluid through such a pipe, the fluidmay be heated and thereafter used as a source of energy.

Other objects are to provide a protective layer on the innermost surfaceof such a liquid pipe that will minimize undesired reactions between thepipe surface and the media in the interior of the pipe and that willminimize loss of material from the interior pipe surface due tovaporization; and to provide interposition layers that minimize orreduce reactivity between adjacent layers in the pipe wall by use ofsubstances which are nonreactive at high temperatures.

SUMMARY OF THE INVENTION The present invention is characterized by thepresence of high temperatures up to the order of 3000 K. and even higherin some applications by use of concentric cylinders which provide layersof metallic or non-metallic substances that will maintain theirconguration even when heated to their liquid state. The heat may beapplied from an external source, or one or more of the layers may serveas the heat source. One feature resides in the provision of a protectivelayer having a high boiling point and low vapor pressure. Anotherfeature resides in providing several different metallic or non-metallicsubstances, all of which have high boiling points and each being in adifferent layer and remaining in such a configuration even when heatedto melting temperatures and thereafter allowed to cool.

Where one of the layers is capable of supporting a nuclear reaction andhence contains a ssionable material such as uranium, it is advantageousto provide adjacent layers that serve to prevent loss of the uraniumthrough vaporization or migration of the uranium to the extent the chainreaction is stopped. Introduction of substances to be heated may servealso as a means of cooling the apparatus.

Chemical reactions between the substances of various layers may beminimized by using materials which do not form at high temperaturesstable compounds such as carbides or oxides, and these materials maysometimes be used in very thin layers as an interposition layer at theinterface between two thicker layers of a liquid metallic andnon-metallic substance. This interposition layer may have a densityhigher than that of the supporting layer.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagrammatic pictorial view ofa rotating pipe showing an outer solid body containing severalconcentric inner layers which may be in a liquid state and of differentmaterials;

FIG. 2 is an elevation in section of a barrel and frame for anelectrical liquid pipe apparatus;

FIG. 3 is an elevation in section of a barrel and frame for a plasma jetliquid pipe apparatus;

FIG. 4 is an elevation in section of a barrel and frame of a furtherstructure embodying three concentric layers of different materialswhich, when heated, may be in liquid form, together with means forremoving the heat;

FIG. 5 is a view illustrating the condensation of liquid alumina on awater-cooled aluminum tube; and

FIG. 6 is an enlarged view of a portion B of FIG. 5.

DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 shows diagrammatically amulti-layer pipe 10 that embodies the present invention. The thicknessesof the various layers are not drawn to any particular scale, since thedrawing is to illustrate qualitatively the relative positions of thevarious layers. The inner three concentric layers 12, 14, and 16 aredifferent materials which usually are solid at room temperature butwhich become liquid at elevated temperatures. Layer 18 may be a somewhatsolidified layer of the same material as layer 16. Layer 20 is a bodythat remains solid and can be regarded as a refractory lining.Refractory materials suitablel for use as layer 20 include aluminumoxide bubbles and bricks, or Thermax (trademark) carbon, zirconia,beryllium oxide, calcium oxide, and many other refractory materials. Atthe center of the liquid pipe and inside of layer 12, free space isprovided for confining and conveying heated gases or other materials.When the temperature at the central free space exceeds the meltingternperature of the innermost layer 12, it is necessary that the entirepipe be subjected to rotation as designated by arrow 22 to provide acentrifugal force of such a magnitude that it overcomes the force ofgravity. This then holds the liquid layer(s) in the concentricconfiguration to provide what is referred to as a liquid pipe.

FIG. 2 illustrates an embodiment wherein the heating source is anelectrical resistance material that carries an electrical current from asource 32 of electrical power. The apparatus has a base 34 and a pair ofsupports 36 and 37 with journals 38 through which the ends of shafts 40and 42 of conductive material are mounted for rotation. Pulley 44 isshown on shaft 42 and rotational force may be provided as by motor -46and belt 48.

A pair of blocks 50 and 52 of a material such as graphite, which is bothheat resistant and electrically conductive, may be joined to turn withshaft 40 and 42. Extending between blocks 50 and 52 is a pipe which mayembody certain of the features of the present invention.

As illustrated, the pipe comprises two layers 30 and `54. Layer 30 maybe the electrical conducting layer, for example, liquid metal, and layer54 an electrically non-conducting material. Outside pipe 54, a suitablebody 56 of insulation such as Thermax (trademark) may be provided thatis held in place, as by a cylindrical frame 58.

Near the ends of shafts 40 and 42, slip ring connections 60 and 62,capable of carrying high current densities, are provided. These may takethe forni of copper discs which contact a liquid metal pool 64, and thetwo pools may be connected by leads 66 and 68 to opposite terminals ofpower source 32.

When direct current is used, the magnetic field created by the largeelectric current passing through tube 30 when in a liquid stateconstricts and finally pinches off the liquid, thus breaking thecircuit. One known method to counteract the pinch effect is by using acentrifugal force greater than the pinch pressure.

When using centrifugal force to maintain continuity, a relationship hasbeen developed which relates rotational speed needed to counteract thepinch effect created by the magnetic field. The relationship was foundto be as follows:

wherein:

S=angular rotation in revolutions per minute of the rotating pipe,

A=current strength in amperes,

Rzinner radius of the pipe in centimeters,

0=thickness in centimeters of the liquid conductor layer 30, and

Dzdensity of the liquid conductor metal 30 at the operating temperaturein g./cm.3.

For example, at a current of 1,000 amperes in a tube where the radius(R) is 3.5 centimeters, the thickness of the liquid metal (0) is 0.30centimeters, the density (D) is 7 g./cm.3, the angular rotation neededto equal the force created by the magnetic pinch effect is 137.5revolutions per minute. Thus, at r.p.m.s higher than 137.5 the currentwill continue to heat the liquid metal, while below this r.p.m. rate,the current will be interrupted by the magnetic pinch.

In the construction of the apparatus of FIG. 2, layer 30 can be, forexample, a material such as mercury which is liquid at room temperature.Of course, if mercury is used in a practical application, steps wouldhave been taken to increase the pressure or otherwise the maximumtemperature would be limited by its comparatively low boiling point.Rotation causes it to assume the form of a liquid pipe. Other materialswhich are solid at room temperature can be inserted initially as a rodor as a hollow pipe. Since rotation occurs during the time thetemperature exceeds the melting temperature, the material will assumethe form of a cylinder. When cooled again to a lower temperature, thematerial will remain in the form of a pipe.

Uses of this liquid pipe at temperatures above the melting points of theelectrical resistance material include the heating of one or more gasessupplied to the input to the hollow shaft at 42 which can be exhaustedat the other end for purposes of a heat producing device or for thecarrying out of chemical reactions requiring high ternperatures.

Referring again to FIG. 1, if the liquid pipe is to be used as achemical reactor and the source of heat is, as illustrated in FIG. 2,the electrical resistance of one of the liquid layers, an inner layer12, which might have not only the purpose of cutting down the vaporpressure of the electrical resistance heating layer 14, but which mightalso essentially chemically protect layer 14, could be used. Forexample, a liquid oxide such as liquid alumina, zirconia, or thoriacould be used as layer 12.

The density of layer. 12 should be less than the density of layer 14 toavoid intermixing of the substances when both are liquid and arerotating at a velocity sufficient to maintain the configuration of apipe as illustrated in FIG. 1.

It is contemplated by the present invention that the electricalresistance heating layer 14 may be supported on one or more furtherlayers 16 and 18 (see FIG. l) which may also become liquid at the hightemperatures reaching during operation of the furnace. The density ofthe further layers when in a liquid state should normally be greaterthan the density of layer 14.

Where the substances of layers 12 and 16 would undergo an undesirablereaction during the operation of the furnace at their interface, layer14 may be provided as an interposition layer which will be described ingreater detail below. It is possible to make layer 14, if sufficientlythin, float on layer 16 even though the density of layer 14 is `greaterthan the density of layer 16, and still prevent an undesirable chemicalreaction between layers 12 and 16.

Referring now to FIG. 3, an embodiment of this invention is illustratedwhich comprises a liquid pipe that may be similar to the pipeillustrated in FIG. l. The base 80 supports rings 82 and 84 that carrybearings 88. Any suitable drive mechanism can be used for rotatingpulley 90 which may surround the liquid pipe supporting frame member 92.Frame 92 is shown surrounded by a jacket 94 for a coolant such as water.

The pipe section of the apparatus consists of a number of concentric,coaxial tubular layers forming a pipe, as shown in FIG. l, encased inframe member 92.

The source of heat here illustrated is a high temperature plasma jet 96operating in the range of 5000" to 25,0020o K., using a noble gas suchas helium or argon. The technology of plasmas and electric arcs isdescribed by W. Finkelburg and H. Maecker in Handbuch der Physik, S..Flugge (Springer, Berlin, 1956), vol. 272, pp. 254-444.

The flow of gas may be from about 0.1 to about 10 s.c.f.m. Theelectrical energy input may be up to 100 kilowatts or more.

The ratio of the vapor pressure of the container material to the totalpressure can be adjusted, if desired, by operating the plasma jet in aliquid pipe at a high total pressure. Thus, apparatus is provided toextend inorganic chemical research, particularly on chemical reactionsin liquid phase (for example, between the container and any addedsubstance lighter than the container), to much higher temperature range.

To obtain such a liquid pipe apparatus for conducting high temperatureresearch, tubes of various compositions may be successively melted inthe rotating pipe by being heated for a suitable time in the plasma jet.The metals of different densities will form cylindrical bands or layersthat are sharply defined and separate. The materials having lowerdensities are relatively easily positioned on materials having heavierdensities which are in a liquid state.

The range of rotations is from 500 to 2,000 rotations per minute. Theactual speed of rotation depends on the radius of rotation, and be suchthat the liquid is subjected to l to g.

It has been found that a liquid 14 can be used as an interface orinterposition layer between layers 12 and 16 to minimize chemicalreactions between them, as discussed above. I have found that metalswhich, although they are denser than liquid 16, can be made to float onliquid 16, and to act as a suitable barrier between layers 12 and 16. Toillustrate the above further, the following laoratory experiment isprovided.

About 250 grams of an equal molar mixture of sodium iodide and potassiumiodide were placed in a 300 cc. Vycor beaker and melted in abutane-oxygen flame. The melting point of the salt mixture is about 600C.; it was heated ot about 680 C. at which temperature the density ofthe salt mixture is 3.29 g./cm.3. On top of this mixture, about 250grams of aluminum metal was melted. (The 6 melting point of purealuminum is 660 C.). It floated on the salt since its density is 2.4g./cm.3 at its melting point. A continuous stream of argon was passedinto the free space above so as to prevent the oxidation of thealuminum.

In this case, the interposition substance selected was liquid tin whichwas melted in a Vycor tube with a narrowed down tip closed by means of aVycor rod. (The melting point of tin is 232 C.)

The tip of the Vycor tube was placed a few millimeters above the liquidaluminum/ salt interface and a few centimeters of liquid tin were slowlyadded to the liquid aluminum metal. This liquid tin spread in the liquidaluminum layer and did not drop to the bottom, although its densityequals 6.75 g./cm.3 at this temperature. However, if the tip of theVycor tube was then lowered below the aluminum/ salt interface, theliquid tin dropped right away, as expected to the bottom of the beakerin the form of a metallic globule.

The whole melt was allowed to cool down, the salt washed out, and themain metal ingot containing the tin was analyzed. A layer a fewmillimeters thick was sawed off from the bottom of the ingot and wasfound by analysis to contain 46 weight percent tin and 54 weight percentaluminum. At 680 C. this alloy has a density of 3.37 g./cm.3. Thus,while the alloy was denser than the salt, it still floated on the moltensalt, and acted successfully as an interposition substance between thelighter aluminum metal and the heavier molten salt.

Other metals which may be used as an interposition layer are themonetary and noble metals, copper, silver, gold, platinum and iridium.Even though their densities as a liquid may exceed the density of thesupporting layer as a liquid, they may be introduced between twoadjacent layers and remain attached to the boundary between the twolayers.

Referring now to FIG. 4, a further embodiment of the present inventionis illustrated wherein the high temperature is generated by nuclearreactions, such as fission chain reaction propagated by neutrons in acylindrical mass of isotope 235 of uranium, isotope 239 of plutonium, orany other fissionable material. In this embodiment, one of the layers,such as layer of the multilayered pipe, is a fissionable material and iscapable of supporting a sustained chain reaction for a period of severalseconds or minutes in the case of an application to produce rocketthrust, or much longer for other applications, such as MHD generatorsand in provoking high temperature reactions. The starting and stoppingof the chain reaction may be by the removal and introduction of neutronabsorbing sustances, such as cadmium or boron. Other layers include asupporting layer 102 which may be in a liquid state in region 104 and ina solid state in region 106. Between layers 100 and 102, an intermediateor interposition layer 108 may be provided, and on the inner surface oflayer 100 a protective layer 110wmay be provided.

An outer cylindrical casing 112 may be provided to surround thesupporting material forming layer 102 and be suitably mounted forrotation on means such as rollers 114. Rotation about axis 116 can beeffected by any convenient means, such as pulley 118, located at theinlet side of the apparatus. Also, at the inlet side, a standardstationary stuffing box 120 is provided. Inside stuffing box 120, astationary pipe 122 may be lmounted which has space or openings providedto accommodate various feeding devices for solids, liquids, or gases. Onthe outlet side, a stationary stuffing box 124 similar to inlet stuffingbox 120 may be provided.

An optional cooling system is illustrated in the upper half of thedrawing of FIG. 4. If the cooling system is used, it would also bepresent throughout the entirety of support layer 102 since the apparatusis symmetrical about axis 116. The illustrated cooling system consistsessentially of a first conduit, 126 for circulating a cooling uidintroduced through an inlet 128 on stuffing box 120.

Fluid entering inlet 128 travels through a suitable groove 130 to enterconduit 126 and follows the direction of the arrows to be ejected intothe central open portion of the apparatus at outlet 132. A similarcooling system may be provided at the outlet end of the apparatus thatis composed of inlet 134, conduit 136, and outlet 138. The function ofconduits 126 and 136 may be for purposes other than cooling, such as topreheat substances that are to be introduced into the heated stream ofgas.

Table I from the published literature gives typical data for the normalboiling points and melting points of some high boiling temperaturemetals and their corresponding heats of vaporization and of fusion. Itis evident from the table that the heat required to vaporize a liquidmetal is roughly about 25 times greater than the heat of fusion. Thus,to vaporize the liquid metal, a large amount of heat has to be added tothe system either by the nuclear reaction or, in the case of electricalresistance heating, by the electrical current, as compared to therelatively small amount of heat that has to be taken out by cooling inorder to maintain the metallic substance in a solid state at its edges.

The same theoretical considerations apply to oxides, carbides, nitrides,and other ceramic materials, and although there is no experimental dataavailable at present on the heats of vaporization and of fusion in anyway comparable to the data in Table I on liquid metals, it is evidentthat the heat of fusion is much less than the heat of vaporization.

The vapor pressure of uranium at 40G-0 K. is 0.21 atmosphere, thusgiving it a tendency under high temperature operation to vaporizereadily and mix with the gas flowing through the interior of theapparatus. It is, of course, evident that the loss of uranium throughthis process would quickly stop the reaction since control of thenuclear chain reaction is importantly influenced by the mass of uraniumpresent. In the illustrated embodiment, layer 100 is assumed to beuranium and a protective layer 110 is therefore provided to reduce therate of vaporization of uranium.

One of the desirable properties of the material forming protective layer110 is that it has a much lower vapor pressure than uranium, thereby toreduce the rate at which this layer vaporizes and is lost into the gasespassing through the center of the apparatus. This material normallyshould be selected to have also a lower density than that of uraniumsince, as pointed out previously, the inner layer must in effect floaton the next outer layer. Materials which can advantageously be used asthe protective layer 110 because of their high `boiling points and lowdensity as compared with that of uranium are given in Table II. Iftungsten is used, small amounts of molybdenum can be added which willlower its density so that it will be less dense than uranium. The sameapplies to rhenium.

From the standpoint of nuclear properties, one of the more importantconsiderations is the neutron capture Cross section of protective layer110. Niobium, zirconium, and molybdenum and certain isotopes of tungstenhave comparatively low capture cross sections on the order of 1 barn orless, whereas tantalum and rhenium and other isotopes of tungsten havemuch higher cross sections.

Isotope 184 of tungsten has a neutron capture cross section of about 2barns. The same gaseous diffusion equipment can be used to producetungsten enriched in isotopes 184 by working WFG as is used to produceuranium enriched in isotope 235. The vapor pressure of tungsten at 4000K. is 4.62 104 atmospheres and its boiling point is about 5800 K. Thus,by using ltungsten, the vapor pressure of the exposed surface layer inthe interior of the liquid pipe is some 450 times smaller than if pureuranium were used. It follows that by using a layer of tungsten only afew millimeters thick, the life of the apparatus will be increasedsignificantly as compared with the life of operation at hightemperatures Without such a layer.

Summarizing, then, the principal layers of the liquid pipe, asillustrated in FIG. 4, are the heat generating layer containing theiissionable material such as isotope 235 of uranium; the protectivelayer having a density not greater than that of uranium, a vaporpressure lower than uranium, and a neutron capture cross sectionsuiciently low to allow the chain reaction to proceed; and finally, asupporting layer 102 to be next described.

The supporting layer may be any suitable substance that can withstandthe high temperatures generated in layer containing the iissionablematerial. Refractory materials in the form of bubbles, beads, and inepowder, and composed of tine substances such as carbon in the form ofgraphite, A1203, BeO, ZrO2, ThO2, CaO, and others that havecharacteristics of refractory materials may advantageously be used. InFIG. 4, layer 102 is illustrated as being composed of a liquid portion104 and a solid portion 106 separated by a dotted line 140. The materialbetween the solid portion 106 and casing 112 may be an extension of therefractory material used for layer 102 and contain the fluid conduits126i and 136 described below.

In the selection of a particular material as a supporting layer 102,consideration must be given to the chemical reactions which may takeplace between the uranium containing layer 100 and the elements orcompounds present 1n supporting layer 102. Some elements are known to bemuch less reactive than others at high temperatures. Platinum, failingto form either a stable carbide or a stable oxide, is a desirablematerial for layer 102 except for the fact that liquid platinum has adensity of about 19 g./cm.3 at its melting point of about 2000 K. It isdesirable to use platinum either as a supporting layer 102 or as aninterposition layer 108. The advantage of considering platinum as aninterposition layer 108 is that a thin layer can be floated at theinterface between two liquid metals even though its density is greaterthan the density of the material forming layer 102.

The significance of the foregoing is that it is not essential to haveall the materials of the pipe positioned according to their respectivedensities, i.e., with the liquid of layer 12 (see FIG. l) having thelowest density and the liquid of layer 16 having the highest density.Also, it makes possible the `use of two materials in nearly adjacentlayers that would undesirably react with each other in course of theoperation of the device, but this reaction can be prevented by thepresence of a comparatively nonreactive material as an interpositionlayer which can be very thin.

Thus, in the embodiment of FIG. 4, the interposition layer 108 isillustrated as being between the main layer 100 and the supporting layer102, while in the embodiment of FIG. l, the interposition layer 13 isillustrated as being between the main layer 14 and the protective layer12. In either case, the purpose of the interposition layer is to reducethe reactions between the adjacent layers. Hence, it should be selectedfrom the monetary and noble metals such as copper, silver, gold,platinum, or iridium. The thickness of the interposition layer, ifformed of material having a higher liquid density than that of thematerial on which it floats, must be very thin, eg., in terms ofmillimeters.

One of the monetary or noble metals may be used as the entire supportinglayer 102 rather than merely as an interposition layer as discussedabove. After it was established by experiment that liquid iron carbide,or Fe3C, and liquid silver, or Ag, form a new practically immisciblesystem at 2200 K., it was found that by adding uranium dicarbide, or UC2to this system at 2000- 2500 K., the uranium dicarbide dissolves in theiron carbide layer and that only a small amount of carbide dissolves inthe silver layer. The analysis results of the two layers at 2000 K. wereas follows:

TABLE IIL-COMPOSITION OF LAYERS More dense Ag layer Wt. Percent Lessdense FegC-l-UCZ layer Wt. Atomic Percent Percent Atomic Percent TABLEIV.-COMPOSITION OF LAYERS More dense Au layer Wt. Atomic Percent PercentLess dense Fe3C-I-UC2 layer Wt. Atomic Percent Percent The ratio of U inupper layer to U in lower layer at this higher temperature is about 15.

Liquid uranium dicarbide, or UC2, has been iloated at 3000 K. on liquidW2C. After 10 minutes at 2950" K., the upper and lower supporting layershad the following composition:

TABLE V.-COMPOSITION OF LAYERS Less dense U02 layer Wt. Atomic PercentPercent More dense W2C layer Wt. Atomi Percent Percent It will beobserved that as the temperature increases, the diffusion of uraniuminto the supporting layer increases. However, where the apparatus isintended to operate for only short intervals of time, such as in rocketthrust applications, the temperature of the layers may not reach themaximum temperatures or at least not operate at such temperatures overextended periods of time.

For steady state applications, the selection of specific materials willdetermine the optimum temperature of operation consistent with therequirements of other parts of the system. Operation of this apparatuson the order of 2000 to 3000 K. offers many advantages not attainable byother sources of energy.

To construct the apparatus, one may calculate or determine fromempirical tests the general configuration the layers should desirablyhave when in a liquid state and fabricate from solid materials theseveral layers that are desired. During assembly, the interior of thepipe can be -filled with a neutron absorbing material in a liquid orgaseous state to prevent premature start-up of the chain reaction. Whenit is desired to start the reaction, the neutron absorber may begradually withdrawn and control eifected in any suitable manner of whichmany are known to those skilled in the art. For example, gases passingthrough the center of the pipe may include elements having high neutronabsorbing properties, or neutron reiiectors can be provided on theoutside of the uranium pipe and their eifective neutron reilectiveproperties modified to change the multiplication factor of the core.

Once the nuclear chain reaction is started, it may be stopped bychanging any of the factors which are essential to the reaction.Introduction of heavy concentrations of neutron absorbers into thecenter of the pipe, as a gas, liquid, or solid, can be effective to stopthe reaction. Also, removing reflectors to thereby allow an increaseinthe escape of neutrons from the exterior of the uranium mass may alsobe used.

In operation, the material forming protective layer may be lost due tovaporization and contact with other substances flowing through theapparatus. New make-up material may be added during operation of theapparatus for replenishment of the lost material through inlet feeder122.

Uranium may be added at the same time. As it is heated and becomesliquid, the uranium will diffuse through layer 1-10 because of thegreater density of uranium.

In the apparatus of the present invention, it is important that the endsof the pipe remain solid even though the central portions become liquid.Hence, it is advantageous to have a cooling arrangement such as thepiping arrangement illustrated in FIG. 4. By locating the cooler portionof conduits 126 and 136 adjacent the ends of the pipe section, thematerial on the outer side of dotted line may be kept solid, while thematerial on the inner side of dotted line 140 is liquid.

The insulating material between supporting layer 102 and outer casing112 and through which the conduits extend may advantageously be thesolid substance of layer 102 in the form of bubbles, beads, fine powder,or any number of available refractory materials like C graphite), A1303,BeO, Zr02, F11h02, CaO, and others.

One of the products which can be produced by high temperatures createdin a high temperature furnace is alumina vapors. To illustrate theextent of the eiiiciency of high temperature cooling, the followingobservations have been made while condensing alumina vapor having anormal boiling point of 3800 K. and a melting point of about 2050 C. or2320 K. With reference to FIGS. 5 and 6, the U-shaped tube 150 is ofaluminum and connected to provide for the circulation of water. Theinterior of the liquid pipe in which U-tube is mounted contains vaporsof A1303 at a temperature of about 3800 K. It has been found thatimmediately on the outer surface of the aluminum tubing, there is aformation of Al2O3 in both a solid and a liquid state.

With reference to FIG. 6, which shows to an enlarged scale only a singlewall of the aluminum tube of FIG. 5, there is formed on the outersurface of tube wall 150 an A1203 powder layer 152. Next there appears asolid crust 154 of A1303. Finally, on the extreme outer surface, liquidA1203 forms. Thus, over a distance of 0.5 to 0.8 cm. (see FIG. 6) thetemperature falls from about 3800 K. in the alumina vapor, to about 300K. in the water flow; therefore, the temperature gradient is from about7000 to about 4400 K./cm. This demonstrates that very high temperaturematerials can be contained by conventional methods of cooling.

With reference to FIG. 4, the coolant may be introduced through thesolid substance of layer 102 which, as pointed out above, may be in theform of bubbles, beads, or ne powder, and allowed to pass directly tothe interior of the hollow pipe. A liquid coolant may also be admittedthrough inlets 128 and 134. After the coolant is preheated, it may iiowdirectly to the central opening of the apparatus, and be introduced intothe gas stream iiowing therethrough, or of course removed from thesystem as may be desired. Because of the heating which occurs inside thereactor, the amount of coolant that flows into inlet 128 on the coolside of the reactor can be made to be approximately 100 times greaterthan the amount which iiows into inlet 134.

Instead of the coolant being merely an inert gas or liquid which is useddirectly in the exhaust, the coolant may be a substance which whenheated dissociates into elements that are in a liquid or gaseous state.The input materials may also be applied at 122 as a gas, a liquid, or asolid. The temperature within the apparatus and the length of time thematerial remains in the apparatus determines the quantity of heat thatis applied to the material. Such elements, when heated, may be allowedto cool in a condensing unit connected to the outlet of the reactor unitof the present invention, and thereby recovered.

One further important technical advantage is that when the layers areliquids, the quantity of the substance in the various layers can bechanged during operation of the apparatus. Specific ingredients can beadded when in the form of a solid, a liquid or as a gas or vapor.Inlgredients can be withdrawn by evaporation or by rernoval while in aliquid state.

In summary, the apparatus of the present invention serves as a containerfor a high temperature and may itself be a furnace, as illustrated bythe several embodiments described. The various layers may be formed ofdifferent substances depending upon Whether the source of heat is anelectrical resistance, an oxidation of an organic or inorganic material,or a nuclear reaction. The heated gases passing through the device maybe used for MHD generators, rocketry, or in any application where hightemperatures are required. Or a confined chamber may be provided forcausing chemical reactions.

The main layer may be protected against vaporization by use of a layerhaving a lower vapor pressure and against chemical reactions by use ofnonreactive materials. Liquid oxides, such as liquid alumina, zirconia,or thoria, are comparatively nonreactive in an oxidizing atmosphere. Theliquid pipe reactor of the present invention may be used eitherhorizontally or vertically (if suiicient centrifugal force is provided),as may be desired.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are, therefore, to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than the foregoing description,and all changes which come within the meaning and range of equivalencyof the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. A high temperature furnace comprising a frame mounted for rotationabout an axis passing through said frame; means on said frame forsupporting a. tubular member coaxially of said rotational axis, saidtubular member having a cylindrical wall comprising at least twoconcentric layers with one of said layers serving as a source of heatfor said furnace, and the one of said layers located on the innersurface of said tubular member formed of a substance having a liquidvapor pressure and a liquid density that are both lower than the liquidvapor pressure and liquid density of the other layer, and wherein theheating layer comprises a substance capable of supporting a neutronchain reaction; and means for passing a uid to be heated through saidtubular memberl 2. The high temperature furnace of claim 1 furthercontaining an interposition layer between said heating layer and theother layer, the substance of said interposition layer having theproperty of not reacting when in the liquid state with the substance ofsaid heating layer.

3. The high temperature furnace of claim 1 wherein the heating layerincludes uranium and the substance forming the other layer is located onthe inner surface on said tubular member and is selected from the groupconsisting of niobium, zirconium, hafnium, molybdenum, tantalum,tungsten and mixtures thereof.

4. The high temperature furnace of claim 1 wherein the heating layercontains uranium and is supported on a further layer, and the otherlayer is located on the inner surface of said tubular member.

5. A high temperature furnace comprising a frame mounted for rotationabout an axis passing through said frame; means on said frame forsupporting a tubular member coaxially of said rotational axis, saidtubular member having a cylindrical wall comprising at least twoconcentric layers with one of said layers serving as a source of heatfor said furnace, and the one of said layers located on the innersurface of said tubular member formed of a substance having a liquidVapor pressure and a liquid density that are both lower than the liquidvapor pressure and liquid density of the other layer, and wherein theheating layer comprises a substance capable of supporting a neutronchain reaction; means for passing a fluid to be heated through saidtubular member; conduits located about said tubular member for thecirculation of a uid; and means for discharging said last mentionedfluid to be intermixed with the iiuid passing through the tubular memberto be heated.

6. The high temperature furnace of claim 5 wherein the heating layer issupported on a further layer which when in a liquid state has a densitygreater than the liquid density of the substance forming said heatinglayer and wherein the other layer is located on the inner surface ofsaid tubular member.

7. The high temperature furnace of claim 6 further containing aninterposition layer between said further layer and said heating layer,the substance of said interposition layer having the property of notreacting when in a liquid state with the substance of said heatinglayer.

8. The high temperature furnace of claim 7 wherein the substance of saidinterposition layer has the property of not forming stable oxides orcarbides when in a liquid state, and further has a liquid densitygreater than the liquid density of the substance forming said furtherlayer, but being suiciently thin to remain at the interface betweenfurther layer and said heating layer.

9. The high temperature furnace of claim 8 wherein the interpositionlayer is platinum, the heating layer includes uranium, and the fourthlayer comprises a substance selected from the group consisting ofgraphite, A1203, BeO, ZrOz, ThO2 and CaO.

10. The high temperature furnace of claim 9 wherein the substanceforming said other layer is selected from the group consisting ofniobium, zirconium, hafnium, molybdenum, tantalum, tungsten and mixturesthereof.

11. A high temperature furnace comprising a frame mounted for rotationabout an axis passing through said frame; means on said frame forsupporting a tubular member coaxially of said rotational axis, saidtubular member having a cylindrical wall comprising at least threeconcentric layers with one of said layers serving as a source heat forsaid furnace, said heating layer comprising a substance capable ofsupporting a neutron chain reaction, the second of said layers beinglocated on the inner surface of said tubular member and formed 0f asubstance having a liquid vapor pressure and a liquid density that areboth lower than the liquid vapor pressure and liquid density of saidheating layer, and the th'ird of said layers supporting the heatinglayer, and which when in a liquid state has a density greater than theliquid density of the substance forming said heating layer.

12. The high temperature furnace of claim 11 wherein the heating layerincludes uranium, and which further comprises a fourth outer layer ofgraphite.

13'. The high temperature furnace of claim 11 wherein the substance forforming the inner layer is selected from the group consisting ofniobium, zirconium, hafnium, moly-bdenum, tantalum, tungsten andmixtures thereof.

14. The high temperature furnace of claim 11 further containing aninterposition layer between said supporting layer and said heatinglayer, the substance of said interposition layer having the property ofnot reacting when 14 15. 'I'he high temperature furnace of claim 14wherein the interposition layer is platinum, the heating layer includesuranium, and an outermost layer comprises a substance selected from thegroup consisting of graphite, niobium, zirconium, hafnium, molybdenum,tantalum, tungsten and mixtures thereof.

References Cited UNITED STATES PATENTS 3,25 7,196 6/1966 Foex 75--103,286,012 11/1966 Foex 13-1 3,246,069 4/1966 Maynord 26-255 1,831,31011/19'31 Lindemuth 164-81 BERNARD A. GILHEANY, Primary Examiner H. B.GILSON, Assistant Examiner U.S. Cl. X.R.

in a liquid state with the substance of said heating layer. 20 13--1

